It is known that hydrocarbon mixtures comprising paraffinic and aromatic compounds can be separated by liquid extraction through the use of an organic solvent. The selection of an organic solvent for the particular extraction process must take into consideration a number of factors. Such factors include selectivity, capacity, recoverability, density, interfacial tension, corrosivity, chemical reactivity and stability, viscosity, toxicity and cost.
The use of N-hydroxyalkylpyrrolidones for separating aromatics and paraffinic compounds has previously been disclosed in U.S. Pat. No. 3,157,592. The process there disclosed is carried out at atmospheric pressure and at temperatures in the range of 5.degree. to 60.degree. C.
In most processes for the solvent extraction of aromatics contained in a mixture with paraffinic compounds, separation of the aromatics from the solvent usually requires distillation at an elevated temperature. In such a process, operating the extraction step of the process at an elevated temperature maximizes the efficient use of energy. Solvent selection for use at elevated temperatures poses several problems. Higher temperatures, while increasing the loading capacity of the solvent, tend to decrease its selectivity. In such an extraction process as this, water is commonly used to control selectivity. However, while increasing the water content will increase the selectivity of the solvent, the loading capacity of the solvent is simultaneously reduced. As a result of these conflicting effects, as well as the other previously mentioned factors which must be considered, very few solvents have really been found suitable for the efficient extraction of aromatics contained in a mixture with paraffinic compounds at elevated temperatures.
Accordingly, it is an object of this invention to provide an improved process for treating a hydrocarbon mixture to selectively separate the aromatic and paraffinic components thereof by a liquid-liquid solvent extraction of the aromatics at elevated temperatures. Other objects will become apparent from the description of the invention.